A dialysis machine of the known type comprises a first circuit for blood circulation, connected, when in use, to the circulatory system of a patient, a second circuit for the circulation of dialysate, and a blood treatment unit, through which the first circuit passes the blood and the second circuit passes the dialysate.
The blood treatment unit comprises a semi-permeable membrane which, when in use, separates the dialysate from the blood and permit the exchange of ions between the dialysate and the blood and the transfer of some of the blood plasma through the membrane.
The first circuit comprises a withdrawal branch located up-line from the blood treatment unit and a return branch located down-line from the blood treatment unit, while the machine comprises a peristaltic pump located in the withdrawal branch to convey the blood extracted from the patient to the blood treatment unit.
More in general, extracorporeal blood circuits are used to move blood outside the body: blood is typically pumped through tubes and arterial and venous bubble traps of disposable tubing sets connecting the patient to the blood treatment unit, for instance a dialyser mounted on the dialysis, or a treatment unit of another type (hemofilter, ultrafilter, hermodiafilter, plasmafilter, etc.) associated to a corresponding blood treatment machine.
It is also known measuring haemoglobin concentration in the blood circuit of a dialysis machine; a known way of determining the concentration of haemoglobin in the red corpuscles during the dialysis treatment (by means of high accurate measurements of an intrusive kind) requires a laboratory examination with hemolysis of blood samples taken during the dialysis session. Other dialysis machines enable non-intrusive measurements of the haemoglobin concentration to be made within the machine.
The non-intrusive measurements made within the machine are less accurate than laboratory measurements, but have the advantage of being provided in real time in such a way that the operating parameters of the dialysis machine can be corrected instantaneously.
Italian Patent IT 1240489 discloses a method of measuring the haemoglobin concentration within the machine in a non-intrusive way, by measuring the absorption of electromagnetic waves crossing the blood flowing in the withdrawal branch of the first circuit.
In order to implement this method the blood circuit having a withdrawal line, a return line and the bubble trap in the withdrawal line, also includes a calibrated and rigid piece of transparent tube rigidly engaged to the outlet of the bubble trap, upstream the connection to the dialyser.
The calibrated piece of transparent tube is designed to be received in an appropriate holder where an emitter and a receiver operate to emit and detect the absorption of electromagnetic waves.
The difference between the emitted intensity and the received intensity of the electromagnetic waves corresponds to the absorption which is correlated with the haemoglobin concentration by a specific relation.
U.S. Pat. No. 6,794,194 discloses another method for measuring the haemoglobin concentration in an extra-corporeal blood circuit of a dialysis machine comprising the measurement of the values of the blood absorption of electromagnetic waves conveyed along a section of said circuit; then the calculation of the haemoglobin concentration is made as a function of the values of absorption and the measured value of blood pressure, blood temperature and the flow rate of the blood along the aforesaid section.
According to this method the rigid piece of calibrated and transparent tube also including a pressure transducer is interposed between the blood pump and dialyser in correspondence of the withdrawal line, in a position where electromagnetic waves sensor and pressure sensor, both born by the machine, operate.
It is also known to use the measure of haemoglobin concentration as a parameter to control the fluid removal from blood.
For instance the ultrafiltration rate can be controlled by measuring the blood haemoglobin concentration upstream the treatment unit and by keeping said haemoglobin concentration or a parameter function of haemoglobin concentration (such as the filtration factor) within a range of acceptability during treatment.
EP 0467805 shows a blood treatment apparatus having an optical/electronic system comprising a LED diode and a photo sensitive sensor capable of receiving the light radiation emitted by the LED and of providing a corresponding electrical signal.
A circuit for processing this electrical signal is able to discriminate when in use whether a tube through which blood flows is placed between LED diode and the sensor.
Finally document WO 2008/90406 discloses an improved rigid tubular transparent element for further improving accuracy of the sensor provided for measuring the hematocrit concentration in the blood.
Moreover it is also known the use of erythropoietin stimulating agents (ESA) which requires a continuous monitoring of the haemoglobin rate in the patient. In the hemodialysis field, the haemoglobin recommended concentration should be comprised between 11 and 13 g/dl.
Generally in the dialysis centres, the monitor of the haemoglobin concentration is made through laboratory tests on blood withdraws from the patient once per month or, in rare cases, once every two weeks.
It is clear that during this time intervals, the haemoglobin value might move from the desired value outside the recommended range.
In this respect a mere frequent analysis of the blood sampled from the patient or a very time consuming specific analysis made by the nephorologist on the haemoglobin variation of each and every single patient can possibly reduce undesired haemoglobin oscillations.